A 53-kg woman eats a 572 Calorie (572 kcal) jelly doughnut for breakfast. (a) Ho

Question

A 53-kg woman eats a 572 Calorie (572 kcal) jelly doughnut for breakfast.

(a) How many joules of energy are the equivalent of one jelly doughnut?


(b) How many steps must the woman climb on a very tall stairway to change the gravitational potential energy of the woman-Earth system by a value equivalent to the food energy in one jelly doughnut? Assume the height of a single stair is 15 cm.


(c) If the human body is only 24% efficient in converting chemical potential energy to mechanical energy, how many steps must the woman climb to work off her breakfast?

Explanation / Answer

1 calorie = 4.184 J

572 Kcal = 572 * 4.184

Enegry = 2.4*10^6 Joules

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Pontnetial Eenrgy E = m g h

E = 2.4*10^6 = 53* 9.8 * h

h = 4620.17/0.15

h = 30800 steps

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part C:

if energy is 24% of 2.4 *10^6

E = 0.24* 2.4 *10^6

E = 5.76 *10^5 J

E = 53 * 9.8 * x = 5.76 *10^5

x = 1109 stairs

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